The Geordie presenter, 42, is currently in rehab after being charged with drink driving.
Ant has already filmed the audition stages of BGT – which starts on Saturday – but he will miss the live semi-finals and final.
Walliams said he sympathises with the star’s plight, and admitted he knows what it is like coping with a personal trauma in the public spotlight.
He said: “Ant and Dec are popular beyond anybody’s imagination, aren’t they? Every single person who comes to the
“I’ve had similar things in my life”
“And they are incredibly relatable and recognisable, and the hard thing about when you’re well-known is that when things go awry in your life, it gets played out in public.
“I’ve had similar things in my life. I remember when my father was dying, I was on the phone to him and people were coming up for selfies. It’s hard because they want you to be smiley and happy but you’re going through something that’s causing you pain.”
Fellow BGT stars also spoke warmly about Ant and sidekick Dec. Britain’s Got More Talent host Stephen Mulhern revealed the lads sent him a video message when he missed filming of auditions after losing his voice.
He said: “I got a lovely message from Ant and Dec. You just feel like you’re missing a limb. I know that sounds ridiculous but because it’s always been us all together, to be missing from that was tough.”
Amanda Holden told how the pair had joined the TV judges travelling from city to city for the auditions on Simon Cowell’s private plane.
She said: “It used to be that Alesha and I would sit with Simon and David, but now Ant and Dec are involved so all the boys sit down one end. But me and Alesha have more fun because we’re up the other end with the PAs and we’ve got the chocolates, bags of crisps and red wine, screaming with laughter.”
And Alesha Dixon said filming BGT was “like coming back to a new school term”.
She added: “The more we
Britain’s Got Talent starts Saturday ITV at 8pm.